When poetry is set to music, you have a powerful tool of communication that can express both ideas and emotions. That is one reason why the Bible has so much poetry in it–and talks about music so much. God knows how He made us. He knows that we can testify to the facts of our faith much more feelingly in poetry and song. See how the process is described in Psalm 28:7:
The Lord is my strength and my shield; my heart trusted in Him, and I am helped; therefore my heart greatly rejoices, and with my song I will praise Him.
But there is an inherent danger with the emotional power of music. In our use of it, we must be careful not to confuse emotional excitation with spiritual exaltation. That replaces legitimate emotion with emotionalism, which may be simply an easily manipulated visceral response to the music. Consider the above verse again, and notice particularly the order of things.
1) The Lord is my strength and my shield; (a basic truth)
2) my heart trusted in Him, (the truth accepted by faith)
3) and I am helped; (faith verified in life)
4) therefore my heart rejoices, (an inward emotional response)
5) and with my song I will praise Him. (an outward expression with poetry set to music)
The order there is significant. The excitement and joy David feels is not generated by the music, but by an appropriation and appreciation of God’s truth, and his experience of God’s blessing. That is how our hymnody should be used, and it ought to be the reason why we sing. It expresses what the Lord has done for us, and how we feel about it. As an old gospel song by Albert Ketchum puts it:
Deep in my heart there’s a gladness,
Jesus has saved me from sin!
Praise to His name–what a Saviour!
Cleansing without and within.
Why do I sing about Jesus?
Why is He precious to me?
He is my Lord and my Saviour,
Dying, He set me free!